1. Technical Field
The present invention relates to a satellite VSAT antenna or a satellite communication antenna for transmitting/receiving (transceiving) multiple polarized waves, and more particularly, to a bidirectional satellite communication antenna for transmitting/receiving multiple polarized waves capable of transmitting/receiving both of linearly polarized waves and circularly polarized waves of satellite signals and of compensating skew caused due to the linearly polarized waves.
2. Description of the Related Art
A reflector antenna is generally used for satellite communication, high-capacity wireless communication, etc. The reflector antenna concentrates signals received using the principal of a reflecting telescope on at least one focus. Generally, focus positions of the reflector antenna may be disposed with a horn antenna or a feed horn. Wherein, the antenna representing the reflector antenna is a parabolic antenna.
The received signals are reflected at the reflector antenna and therefore are transferred into the feedhorn, and the feedhorn transfers signals inputted to the feedhorn through a waveguide into a low noise block down converter (LNB). Further, the low noise block down converter converts the signals received from the feedhorn into the signals at an intermediate frequency band to finally transfer the converted signals into external image reproducing media such as a TV set-top box. On the contrary, transmission signals having intermediate frequencies are changed into high frequency signals through the block up converter (BUC) to radiate the changed signals into the air in the direction of a satellite through the feedhorn and reflector antenna.
The satellite communication antenna or the satellite VSAT antenna performing both of transmission and receipt should minimize interference between transmitting signals and receiving signals. One method for minimizing the interference between the transmitting signals and the receiving signals is that the frequency band of the transmitting signals is differently set with it of the receiving signals. For example, the frequency band of the receiving signals at a band Ku is set to 10.7˜12.75 GHz and the frequency band of the transmitting signals is set to 13.75˜14.5 GHz, thereby to prevent the interference between the receiving signals and the transmitting signals. Further, in case of a band C, the frequency band of the receiving signals is set to 3.4˜4.2 GHz and the frequency band of the transmitting signals is set to 5.85˜6.725 GHz. The other one method, which improves an isolation degree between the transmitting signals and the receiving signals, use differently the polarized wave for the transmitting signals and the receiving signals. For example, the receiving signals use the horizontally polarized wave and the transmitting signals use the vertically polarized wave or, on the contrary, they may be used. On mentioning in more detail, they may use random 2 linearly polarized waves orthogonal to each other according to skew angles of the linearly polarized wave rather than the vertically/horizontally polarized waves. Further, the receiving signals use left hand circularly polarized wave and the transmitting signals use right hand circularly polarized wave or, on the contrary, they may be used.
On the other hand, the vertically/horizontally linearly polarized waves or left/right hand circularly polarized waves are set to the polarized waves used for the transmission/receipt of the satellite communication antenna or satellite VSAT antenna according to regions. Therefore, the polarized waves of maritime/athletic satellite communication (or VSAT) antennas using them should be also set to the linearly or circularly polarized waves. Since polarized wave characteristics are set according the regions in case of the satellite antenna on the ground, the feeder is disposed according to the polarized wave including the circularly polarized wave or the linearly polarized wave. When the low noise block down converter and block up converter suitable for the feeder are used, it is unnecessary to replace the feeder hereinafter. However, in case of a maritime satellite antenna, since the polarized wave characteristics of the satellite are changed from the circularly polarized wave to the linearly polarized wave or from the linearly polarized wave to the circularly polarized wave according the movement of a ship between countries and continents, the linearly polarized wave and the circularly polarized wave should be selectively received. However, in order to selectively transmit/receive the linearly polarized wave and the circularly polarized wave at the moment, it is necessary to replace the feeder suitable for the polarized wave and to perform inconvenient operations such as the reassembling of the low noise block down converter and block up converter.
In particular, in case of a maritime satellite tracking antenna, it was impossible to replace the feeder for the circularly polarized wave and the feeder for the linearly polarized wave with each other without special knowledges about the assemblies and disassemblies of a maritime antenna due to the complexity of the apparatus such as a radome and the antenna environment being pumped by waves.
Further, the transmitting/receiving polarized waves of the satellite communication or VSAT antenna may implement all of the horizontally/vertically linearly polarized waves and the left hand/right hand circularly polarized waves, and the functions capable of automatically compensating the skew angles are surely necessary in case of actuating by the horizontally/vertically linearly polarized waves.
That is to say, on transmitting and receiving with the satellite by randomly linearly polarized wave, the skew angles of compensating errors of the satellite signal polarized and therefore automatically aligning the feeder of the antenna should be controlled in a comparative simple structure.
In case of the linearly polarized wave, distortions of the linearly polarized wave are caused due to Faraday rotation generated in an ionization layer. The difference between the angles of the linearly polarized wave bent by the distortions and original linearly polarized wave is called the skew angles, and the satellite antenna should surely compensate the skew angles in order to minimize the decrease for the transmitting signals and receiving signals.
The skew angles are compensated by rotating the satellite antenna itself by the skew angles in case of the existing case, and the satellite antenna itself is rotated by this scheme. Therefore, the size of the satellite antenna is increased, much manufacturing cost is required, and power loss become much higher.